Why did World War I happen? Several of the oft-cited causes are reviewed and discussed in this analysis. The argument of the alliance systems is inadequate, lacking relevance or compelling force. The argument of an accident or "slide" is also inadequate, given the clear and unambiguous evidence of intentions. The arguments of mass demands focusing on nationalism, militarism, and social Darwinism are also arguably insufficient. They lack indications of frequency, intensity, and process or influence on the various decisions.